Improving the electrical properties of pentaerythritol esters by treatment with magnesium silicate



United States I IMPRGVING THE ELECTRHZAL PROPERTIES OF The present invention relates to a process for the treatment of synthetic plasticizers to improve their electrical properties. More particularly, it relates to a process for improving the electrical properties of a synthetic ester prepared by the esterification of a polyhydric alcohol and a monobasic carboxylic acid which comprises contacting said ester with an inorganic adsorbent.

Esters of polyhydric alcohols and monobasic carboxylic acids have been used for many years as plasticizers for synthetic resins, particularly for synthetic vinyl polymers such as polyvinyl chloride. While these esters have proved to be more than satisfactory plasticizers in many respects, in some applications their electrical properties are relatively poor. Thus, for example, the volume resistivities of such plasticizers are often so low that the plasticizers are not fully acceptable for use in synthetic resins that are to be fabricated for use in certain electrical applications.

In the past, attempts have been made to decolorize various organic esters by contacting them with an inorganic adsorbent such as an activated clay. For the most part, these adsorbent treatments have been applied to naturally-occurring esters such as fatty acid glycerides. In other instances, treatment has been applied to synthetic esters, e. g., esters of o-phthalic acid, but no improvement in electrical properties of these esters has been observed. As far as is known, synthetic esters of polyhydric alcohols and monobasic carboxylic acids have not been subjected to treatment of the type described herein.

It has now been found that synthetic esters of a polyhydric alcohol and a monobasic carboxylic acid, particularly esters of pentaerythritol and monobasic carboxylic acids, can be improved significantly in their electrical properties by contacting said esters with an ice inorganic adsorbent. In accordance with this discovery,

' the invention provides a process which comprises contacting an ester of a polyhydric alcohol and a monobasic carboxylic acid with an inorganic adsorbent for a time of at least about one minute.

Among the inorganic adsorbents that can be used in practicing the invention are naturally-occurring clays of the bentonite, montmorillonite and attapulgite types which have been activated by treatment with an acid or base. Synthetic inorganic adsorbents such as metallic silicates can also be used and, in fact, an outstanding adsorbent is synthetic hydrous magnesium silicate. In addition, inorganic adsorbents such as silica gel, activated alumina and silicic acid are operable. All of these are characteristically silicic, i. e., silicon-containing materials.

In order to illustrate the invention in further detail, the following examples are presented. Partsand percentages are by weight unless otherwise specified.

EXAMPLES 1 THROUGH 22 The plasticizer treated in these examples was pentaerythritol tetrahexanoate. The inorganic adsorbents which were used include MagnesoF [a synthetic hydrous magnesium silicate (MgO.2.5SiO .I-I O) prepared in accordance with U. S. Patent No. 2,393,625 which had a free moisture content of about contained about 2% chlorides calculated as calcium chloride and possessed a particle size of 99-100% through 325 mesh], Super Filtrol (an acid-activated bentonite of particle size -75 +200 mesh), activated alumina (70 and 200 mesh), silica gel (200 mesh) and Florex XXX (a calcined Florida fullers earth having a particle size of 90% through 200 mesh).

The treatment of the plasticizer was carried out by heating the plasticizer to 135 C. and then slurrying it with a predetermined precentage of adsorbent based on the weight of plasticizer for minutes. At the completion of the slurrying, there was added about 2% of diatomaceo us earth (an inert filter aid) and the plasticizer and adsorbent earth were next separated by filtration. Acid numbers, hydroxyl contents, hazen colors and volume resistivities were determined before and after the treatment. The results obtained are presented below in tabular form:

Table I Product characteristics Example Percent Time Temp.

No. Adsorbent adsorbent (min) 0.) Volume Acid No. Percent Hazen resistivity hydroxyl color (ohm-cm.

1 Super Filtrol 5 15 O. 03 0. 350 29. G 2. do 5 15 80 0. 16 0. 32 295 33. 6 5 15 135 0. 59 0. 23 510 39. 2 4 5 10 135 530 31. 5 5 135 540 38. 2 2 15 135 0. O4 0. 22 380 33. 0 6 15 135 O. 01 0. 28 290 74. 7 6 15 135 0. 04 0. 26 285 99.0 7 15 135 0. 01 0. 22 340 174. 0 8 15 135 0. 01 0. 28 310 118.0 10 15 135 0. 02 0. 22 320 149. 0 10 15 20 O. 02 0. 28 285 33. 2 10 15 0. 01 O. 30 290 34. 8 10 10 0. 03 0. 25 310 78. 6 10 30 135 0. 01 0. 28 310 80. 5 in (7 5 15 135 Nil 0. 29 380 41. 7 Activated alumina (200 mesh) 5 15 135 Nil 440 36.6 18 Silica gel 10 15 135 0. 06 0. 20 370 40. 6 19. Florex XXX. 5 15 135 0.05 0.28 260 43.0 20 Silicic acid 5 15 135 0. 06 O. 31 490 24. 4

' INITIAL CHARACTERISTICS OF PLASTICIZER Acid No 1 1 0. 02 Percent hydroxyi 0.025 Hazen color 40 m 0 Vol. resistivity ohm-cm 7 0g 1 u In additional experiments, the plasticizer was treated as above with a given adsorbent, filtered, treated with '4 and monohydric alcohols, thus demonstrating the selectivity of the invention as far as the general chemical a different adsorbent, and then filtered again. The results composition of the plasticizer is concerned. were as follows: The variables which to some extent may affect the Table II Product characteristics Example Percent Time Temp.

No. Adsorbent adsorb- (min) 0.) Volume ent Acid N0. Percent Hazen resistivity hydroxyl color (ohm-cm.

agneso 10 15 1 5 22 Filmy," 5 15 135 0.82 0.35 520 47.1

The data tabulated above show that in every instance an improvement in volume resistivity was obtained. It is further pointed out that the improvement in volume resistivity is independent of improvement in color because in some instances deterioration of color was observed and is also independent of change in acid number because in some instances an increase in acid number was noted. It is significant also that a treatment with two different adsorbents can be used although such treatment offers no particular advantages.

Among the adsorbents, synthetic hydrous magnesium silicate (Magnesol") is outstanding with respect to improvement in volume resistivity, and use of this adsorbent has the further advantages that color is incidentally improved and acid number is unchanged.

EXAMPLE 23 In this example the plasticizer treated was 1,1,l-trimethylolpropane trihexanoate having an initial volume resistivity of 26.6)(10 ohm-cm. Treatment with 5% Magnesol for 15 minutes at 135 C. raised the volume resistivity 49.4)(10 ohm-cm. Treatment with Super Filtrol" for 15 minutes at 135 C. raised the volume resistivity to 43.2 10 ohm-cm.

EXAMPLE A That the improvement in the plasticizers obtained by the process of the invention is not applicable generally to other plasticizers was demonstrated by the treatment of di(2-ethylhexyl) adipate and di(2-ethylhexyl) phthalate by the same manipulative procedures of Example 1. The following results were noted:

degree of improvement of the plasticizers are the amount of adsorbent and the time and temperature of treatment. Of these, temperature has been found to be the most important; the higher the temperature, within reason, the greater is the improvement in volume resistivity. While any temperature below that at which the plasticizer undergoing treatment decomposes or darkens can be used, a temperature of from about 20 to 175 C. is generally used with a temperature of from about to 150 C. being preferred.

The time of contact has been found to have little effect on the results obtained. A contact time of at least about 1 minute(s) is recommended to assure adequate treatment but there is no upper limit on the time of contact.

The amount of adsorbent can be varied widely, it being understood that any finite amount of adsorbent used for any finite length of time will result in some improvement. A recommended minimum amount is 0.1% of the weight of plasticizer while the maximum that can be used is solely a matter of economy and simplicity.

The contacting of the adsorbent and the plasticizer can be carried out by any of several manipulative procedures known to the art. The examples have illustrated contact by slurrying but other equivalent procedures, e. g., percolation, etc., can be used.

The process of the invention is applicable to any plasticizer that is essentially a synthetic complete ester of a polyhydric alcohol and a monobasic carboxylic acid. It is particularly effective when applied to tetraesters Table III Product characteristics Percent Time Temp. Plasticizcr Adsorbent adsorbent (min) 0.) Volume Acid No. Percent Hazen resistivity hydroxyl color (ohm-cm.

Di(2-ethylhexyl) phthalate. :guperi1l%rol 5 1.65 0.03 137 0.716

upcr i ro 5 D0 {u n 5 15 as N11 0.20 Dl(2-ethylhexyl) adipate guper Hrol 5 15 135 0.21 0.07 100 2.28

eupcr ro 5 15 5 D0 5 15 135 0.13 0.05 2.87

INITIAL CHARACTERISTICS OF PLASTICIZERS Of pentaerythritol and carboxyli acids, containing 65 from about 4 to 12 carbon atoms, e. g., n-butyric, Di(2 ethy1 maethy]. n-valeric, n-caproic, caprylic, capric, etc. acids. It is gf g g z ga "also eifective, however, on corresponding esters of polyhydric alcohols, particularly those containing at least Add No 093 three hydroxy groups, such as 1,1, 1-trimethylolethane, gzzrcglllllg%gr0xyl g; 70 1,1,1-tr1methylolpropane, glycerol, dipentaerythritol, tr1- V0l.resistivify dlifri erii 214x10 3. 19x10" pentaerythritol and the like.

What I claim and desire to protect by Letters Patent is: It is apparent from the above results that treatment The Process which comprises Contacting a Synthetic with an inorganic adsorbent can actually detract from tetraester of pentaerythritol and an alkanoic acid conthe electrical properties of esters of dicarboxylic acids 75 taining from 4 to 12 carbon atoms with synthetic hydrous magnesium silicate for at least about one minute to References Cited in the file of this patent increase the volume resistivity of said ester. UNITED STATES PATENTS 2. The process of clalm 1 1n WhlCh the temperature 2 8 N 18 1952 of the ester is from about 20 to 175 C. Halley E 1953 3. The process which comprises contacting the tetra- 5 3 ,289 I ay 1953 ester of pentaerythritol and a mixture of alkyl carboxylic gg iis E2; 1954 aclds having an average cham length of C wlth a 2:776:984 Mention et a1 Jan. 1957 synthetic hydrous magnesium silicate at a temperature of from about 20 to 175 C. and for a time of at least OTHER REFERENCES about one the amqunt of adsorbent being at 10 Kraus, C. A.: The Properties of Electrically Conductleast 0.1% by weight of sa1d ester.

4. The process of claim 1 in which the amount of 19 adsorbent is at least 0.1% by weight of said ester. bassidy, H. G: Adsorption and Chromatography,

Interscience Pub. Co., N. Y. (1951), page 139.

ing Systems, Chemical Catalog Co., N. Y. (1922), pp. 

1. THE PROCESS WHICH COMPRISES CONTACTING A SYNTHETIC TETRAESTER OF PENTAERYTHRITIL AND AN ALKANOIC ACID CONTAINING FROM 4 TO 12 CARBON ATOMS WITH SYNTHETIC HYDROUS MAGNESIUM SILICATE FOR AT LEAST ABOUT ONE MINUTE TO INCREASE THE VOLUME RESISTIVITY OF SAID ESTER. 